Polymer Dispersed Liquid Crystal Layer Research Articles

Multi-field driven thermochromic films with phase change energy storage properties

Phase change energy storage microcapsules (PCESM) are commonly used for energy storage and energy conservation management. The device has the function to absorb and store external energy by doping PCESM. In the field of optoelectronic displays, the multi-field driven thermochromic film (TCF) was driven through continuous action of electric field and temperature field to realize the special display function of TCF. The study presents a multi-field driven thermochromic films with phase change energy storage properties (PCES-TCF). PCES-TCF is constructed by thermochromic liquid crystal layer and polymer dispersed liquid crystal layer. In the performance experiments, the effects of diluent, liquid crystal and PCESM contents on the electro-optical properties of PCES-TCF were mainly investigated. In the film formation experiments, PCES-TCF is driven by the electric and temperature fields for transmittance and color change, while preparing multi-color patterns. The film formation on either rigid or flexible substrates possesses stable phase change energy storage as determined by infrared thermography and differential scanning calorimetry (DSC). PCES-TCF has a strong potential for application by reducing external energy consumption based on enhanced color change time controllability.

Programmable Coloration and Patterning on Reconfigurable Chiral Photonic Paper

AbstractResponsive photonic crystals are widely employed to construct rewritable paper, where patterns are written and erased repeatedly via color switching. The working principle mainly lies in the changes on the lattice constant of periodic structures, which, however, restricts the localized color tuning of the recorded patterns and thus limits multicolor information transfer. Herein, a novel strategy is reported to write, erase, and importantly to tune the colors by developing unique light‐driven cholesteric liquid crystals (CLCs) that possess self‐organized helical superstructures with two structural elements of pitch lengths (lattice constant) and helical axes (reconfiguration). Reconfiguration of the helical axes provides two high‐contrast optical states for writing and erasing by pressure and electricity, whereas precise photocontrol of the pitch lengths contributes to localized color tuning. These features primarily capitalize on the light‐driven CLC with diverse photostationary colors, which is induced by a newly designed binary chiral system and confined in the polymer dispersed liquid crystal layer. Distinct multicolor patterns are mechanically written, optically tuned, and electrically erased on the rewritable photonic paper in a programmable manner. Such photonic paper has potential to record, program, and remember optically addressed images in visualized color information and user‐interactive display technologies.

A 3D display with switchable optimal view distances

Conventional 3D displays have only one optimal view distance (OVD). When observers stay away from the OVD, crosstalk occurs. Therefore, a 3D display with switchable optimal view distances is proposed. The proposed 3D display consists of a scattering modulator, a directional light source array, and a 2D display panel. The 2D display panel is used to provide parallax images. The directional light source array light up the scattering modulator to form a postpositive backlight. The scattering modulator is formed by stacking at least two polymer dispersed liquid crystal (PDLC) layers. One layer in the stack can be set in a scattering state. The others are set in a transparent state. So the scattering PDLC layer will become a postpositive backlight and project parallax images into different spatial directions. Because the PDLC layers in the stack have different distances to the 2D display panel, different OVDs can be provided. A prototype of the proposed display is developed. Experimental results show the proposed 3D display is helpful for crosstalk reduction by switching to suitable OVD.

A Contact-Sliding-Triboelectrification-Driven Dynamic Optical Transmittance Modulator for Self-Powered Information Covering and Selective Visualization.

Triboelectrification-enabled self-powered flexible electronic/optical systems have aroused a new surge of interest in recent years. All-in-one integration of such a system, which could significantly improve its adaptability, operability, and portability, still remains a challenge due to the absence of suitable architectures and integration schemes. Herein, a previously reported self-powered optical switch (OS) is thoroughly remolded and upgraded to a fully integrated contact-sliding-triboelectrification-driven dynamic optical transmittance modulator (OTM). The OTM is constructed with a multilayered structure, comprising a transparent triboelectrification top layer, a SiO2 -spaced polymer dispersed liquid crystal (PDLC) intermediate layer, and a flexible transparent conductive substrate. The working mechanism is that an alternating electric field can be induced once contact-sliding occurs upon the OTM, rendering the PDLC layer immediately switching its initial translucent state to an instantaneous transparent state. As such, a decent dimming range with the relative transmitted light intensity from 0.17 to 0.72 can be achieved at low mechanical thresholds of contact pressure (≈20 kPa) and sliding velocity (≈0.3 m s-1 ). Moreover, for practical applications, demonstrations of information covering and selective visualization are successfully implemented without any extra optical elements nor external power supplies, explicitly showing great potential for the OTM in various self-powered optical interactive applications.

The effect of thickness on electro-optical properties of plastic UV-curable polymer dispersed liquid crystal (PDLC)

We investigated the effect of polymer dispersed liquid crystal (PDLC) layer thickness on morphology and electro-optical properties of plastic UV-curable PDLC films with two nematic liquid crystal mixtures TNO623 and TNO403. The PDLC films were prepared on flexible Indium Tin Oxide (ITO) coated Poly-Ethylene-Terephthalide (PET) supports by UV-polymerization induced phase separation, and the uniform film thickness was insured by plastic micro-spacers. We found that the PDLC layer thickness at the same morphology effects on electro-optical properties of off-state and on-state transmissions, switching voltages and response times.

The Effect of Thickness on Morphology and Electro-Optics of Plastic Thermoset Polymer Dispersed Liquid Crystal (PDLC)

We investigated the effect of PDLC layer thickness on morphology and electro-optical properties of plastic thermoset PDLC films with two nematic liquid crystal mixtures E7 and TNO623. The PDLC films were prepared on flexible ITO-PET supports by thermal PIPS phase separation method and the uniform film thickness was insured by plastic micro-spacers. We found that the PDLC layer thickness has a profound effect on micro-droplet morphology (dimension, number density and weight fraction) and electro-optical properties (off-state and on-state transmissions, switching voltages and response times).

Liquid Crystal Device with Reflective Microstructure for Attitude Control

Liquid crystal devices (LCDs) are proposed as fuel-free attitude control devices for spacecraft. The LCDs consist of multiple thin layers, including polymer-dispersed liquid crystal (PDLC) and a base film that has a microstructure with aluminum deposited onto it. When a voltage is applied to an LCD, the crystals in the PDLC align with the electric field, and incident light passes through the PDLC layer and is reflected by the aluminum coating, whereas it is dispersed by randomly arranged crystals when no voltage is applied. This means that arrangements of LCDs can control both the magnitude and direction of reflection electrically, and they can achieve three-degree-of-freedom attitude control using solar radiation pressure. Because light diffracted by the layers causes optical interference, the PDLC has a polarization effect, and the microstructure shape has manufacturing errors, reflection from LCDs is a complex phenomenon and it must be understood to realize the desired performance." The first sentence all means the reason for the second sentence.

Tunable structure of nanowire-grid polarizer for deep ultraviolet region

As the performance of nanowire-grid polarizer is determined by the characteristic size of nanowire, the polarizer for full ultraviolet (UV) region requires the characteristic size less than 50 nm, which is challengeable to the current fabrication level. In this letter, two pieces of nanowire-grid polarizers sandwiching a layer of polymer-dispersed liquid crystal (PDLC) was proposed as a tunable structure of nanowire-grid polarizer for high performance in deep ultraviolet region with 100 nm of nanowire period. In this structure, the transmittance of transverse electric (TE) mode (TTE) and transverse magnetic (TM) mode (TTM), and also the transmission extinction ratio (Ex) could be tuned by the optical path of the PDLC layer. Assuming the refractive index of PDLC layer could be varied from 1.5 to 1.6 as its applied voltage changed from saturation voltage to zero, we calculated the TTM and Ex, which varies periodically as the PDLC layer refractive index increasing. For a given incident wavelength, the maximums of TTM and Ex could be attained easily by tuning the applied voltage on PDLC layer. The simulation results show that the tunable structure has a short starting wavelength than that of single layer and double-layer structure nanowire-grid polarizer at a given transmission or extinction requirement with same characteristic size of nanowire, because of the constructive interference of TM polarization and the destructive interference of TE polarization in these two layers of nanowire, similar to a Fabry-Perot cavity, which makes it excellent to be applied in deep UV region.

Broadband pH-Sensing Organic Transistors with Polymeric Sensing Layers Featuring Liquid Crystal Microdomains Encapsulated by Di-Block Copolymer Chains.

We report broadband pH-sensing organic field-effect transistors (OFETs) with the polymer-dispersed liquid crystal (PDLC) sensing layers. The PDLC layers are prepared by spin-coating using ethanol solutions containing 4-cyano-4'-pentyl-biphenyl (5CB) and a diblock copolymer (PAA-b-PCBOA) that consists of LC-philic block [poly(4-cyano-biphenyl-4-oxyundecyl acrylate) (PCBOA)] and acrylic acid block [poly(acrylic acid) (PAA)]. The spin-coated sensing layers feature of 5CB microdomains (<5 μm) encapsulated by the PAA-b-PCBOA polymer chains. The resulting LC-integrated-OFETs (PDLC-i-OFETs) can detect precisely and reproducibly a wide range of pH with only small amounts (10-40 μL) of analyte solutions in both static and dynamic perfusion modes. The positive drain current change is measured for acidic solutions (pH < 7), whereas basic solutions (pH > 7) result in the negative change of drain current. The drain current trend in the present PDLC-i-OFET devices is explained by the shrinking-expanding mechanism of the PAA chains in the diblock copolymer layers.

P-69: Studies on 2D/3D Switchable Autostereoscopic Display with Spatial and Sequential Hybrid Control Using PDLC Films

An effective approach to achieve 2D/3D switching in an autostereoscopic display with spatial and sequential hybrid control (SSHC) using polymer dispersed liquid crystal (PDLC) films is proposed. The Monte Carlo method is utilized to analyze the scattering interaction of diffusive PDLC layer within the system. And the experimental result is given for a two-viewpoint SSHC system. The results show that PDLC working as 2D/3D switch is fairly feasible in a directional backlight autostereoscopic display.

Enhanced Adhesion and Transmittance Uniformity in Laminated Polymer-Dispersed Liquid Crystal Films

We propose a two-step UV irradiation procedure to fabricate polymer-dispersed liquid crystal (PDLC) films by lamination. During the first UV treatment, before lamination, the UV-curable monomers coated on one film substrate are solidified through photo-polymerization as the phase separation between the liquid crystals and the monomers. Introducing an adhesion-enhancement layer on the other plastic substrate and controlling the UV irradiation conditions ensure that UV-induced cross-linkable functional groups remain on the surfaces of the photo-polymerized layers. Thereby, the adhesion stability between the top and bottom films is much improved during a second (post-lamination) UV treatment by further UV-induced cross-linking at the interface. Because the adhesion-enhancement and PDLC layers prepared by the bar-coating process are solidified before lamination, the PDLC droplet distribution and the cell gap between the two plastic substrates remain uniform under the lamination pressure. This ensures that the voltage-controlled light transmittance is uniform across the entire sample.

Electronically controlled wavelength‐tunable transmission filter based on metal grating incorporating polymer‐dispersed liquid crystal

A novel narrow-band tunable transmission filter based on a sub-wavelength metallic grating incorporating polymer-dispersed liquid crystal (PDLC) with a tunable range of 47.2 nm is demonstrated. The transmission peak wavelength can be tuned from 1524.9 to 1572.1 nm when the refractive index of the PDLC layer is varied by different applying voltages. More than 95% transmission efficiency can be achieved at the resonant wavelength, while the −3 dB bandwidth is about 1.6 nm. In addition, the resonant wavelength of the filter varies in a linear fashion with regard to the refractive index of the PDLC layer. Hence, a desired resonant wavelength can be selected easily by controlling the applied voltage.

Near-infrared sensitive photorefractive device using polymer dispersed liquid crystal and BSO:Ru hybrid structure.

A near-infrared sensitive hybrid device, based on a Ru-doped BSO photorefractive substrate and polymer dispersed liquid crystal (PDLC) layer, is reported. It is found that the photoexcited charge carriers generated in the BSO:Ru substrate create an optically induced space charge field, sufficient to penetrate into the PDLC layer and to re-orient the LC molecules inside the droplets. Beam-coupling measurements at the Bragg regime are performed showing prospective amplification values and high spatial resolution. The proposed structure does not require indium tin oxide (ITO) contacts and alignment layers. Such a device allows all the processes to be controlled by light, thus opening further potential for real-time image processing at the near-infrared range.

Real-Time Angular Sensitivity Compensation of Guided-Mode Resonance Filter

Guided-mode resonant filters (GMRFs) are promising narrowband filters with high peak efficiency, but their practical applications have been restricted by their natural high angular sensitivity. We investigated the influence of incident angle and azimuthal angle on the spectral response of GMRF, and found that the resonant peaks are mainly influenced by the incident angle. A polymer-dispersed liquid crystal layer was introduced to compensate the shift of resonant wavelength through applying proper voltage in real time, and numerical results show that a large angular compensation range of about ±4.2° can be obtained while maintaining high performance of the spectral response.

Development of passive and active microprism arrays to change the radiation pattern of solid-state lighting

This study implements a compact solid-state lighting chip with changeable illumination map as well as radiation pattern. The lighting chip consists of a microprism array, light-emitting diode (LED) chip and Si carrier. The polydimethylsiloxane (PDMS) and polymer-dispersed liquid crystal (PDLC) layers are respectively employed to implement the passive and active microprism arrays. The specific radiation pattern can be defined by the shape of the passive PDMS-microprism. Moreover, by using the scattering and transmitting modes of the PDLC layer, the PDLC-microprism enables the changing of light shaping by applying voltage. Thus, the radiation pattern can be changed by the driving voltage on the PDLC layer, and the deformable and movable micro optical components are not required. This study has established the low-temperature fabrication and packaging processes to realize the lighting chip, and the damage of the PDMS and PDLC material is prevented. Typical dimensions of the PDMS lighting chip are 5 mm wide, 6 mm long and 1 mm thick, and The PDLC lighting chip is 550 µm thick. The measurement results show that the PDMS-microprism array can change the radiation pattern from a 70° half-maximum viewing angle to 52° and 40° half-maximum viewing angles on two orthogonal axes. In addition, the PDLC-microprism array can change the radiation pattern from 51° and 43° half-maximum viewing angles at 0 V (i.e. scattering mode) to 48° and 33° half-maximum viewing angles at 100 V (i.e. transmitting mode).

Electroluminescent devices with function of electro-optic shutter

The polymer-dispersed liquid crystal (PDLC) was used as a dielectric layer of electroluminescent (EL) device to provide multi-function of electroluminescence and electro-optic shutter. A 50 μm-thick PDLC layer was formed between a transparent electrode and a ZnS:Cu phosphor layer. The electro-optic properties of the EL device were not distorted by the introduction of the PDLC layer. The extraction efficiency of luminescence was improved by more than 14% by PDLC layer. The transmittance of the PDLC was also founded not to be degraded significantly by excitation frequency. Therefore, the electroluminescence of the device was ignited by excitation frequency at a given voltage for full transparency of the PDLC. This device has great potential for applications in transparent displays with the function of a privacy window.

Optical property enhancement of dye‐PDLC using active reflector structure

AbstractThe enhancement of electro‐optical properties in reflective‐type dye polymer dispersed liquid crystal (PDLC) has been achieved by applying an additional white PDLC layer along with dye PDLC layer. This newly modified structure that consists of white PDLC layer and scattering reflector acts as an active reflector. In this practice, an additional arrangement of a polymer barrier layer is made‐up over white PDLC layer, to block the absorption of any solution from dye PDLC. The contrast ratio of this new configuration is almost doubled with low driving voltage and high ON reflectance. Simultaneously, the “off” state has been observed darker than single layer dye PDLC structure. This new configuration can be potentially significant for various display applications such as E‐paper, outdoor billboard, and flexible display. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Type of tunable guided-mode resonance filter based on electro-optic characteristic of polymer-dispersed liquid crystal

A narrowband guided-mode resonance filter (GMRF) incorporating polymer-dispersed liquid crystal (PDLC) is designed. Simulating the characteristics of the filter with rigorous coupled-wave analysis, we find that the resonance wavelength of the new kind of GMRF can be tuned from 672.4 to 698.4 nm by varying the refractive index of the PDLC layer with the applied voltage. Furthermore, the resonance wavelengths vary in a linear fashion with respect to the refractive index of the PDLC layer. Therefore, the desired resonance wavelength can be conveniently selected and tuned in a tuning range of 26 nm by using the applied voltage.

Single‐layered microscale linear‐gradient PDLC material for electro‐optics

AbstractWe report on single‐layered optical material of linear‐gradient microscale polymer‐dispersed liquid crystal (PDLC). E7/NOA65 composite films formed by pulsed UV laser photopolymerization‐induced phase separation exhibit two morphology types, namely a bipolar and a hybrid alignment of liquid crystal droplets. The specific structural properties of the produced PDLC layers, such as the droplet shape uniformity and alignment, as well as the droplet size control through the film thickness, facilitate the efficient control on the electro‐optical (EO) response, thus being of practical interest for EO device applications. (© 2009 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Depth-enhanced integral imaging display system with electrically variable image planes using polymer-dispersed liquid-crystal layers

A depth-enhanced three-dimensional integral imaging system with electrically variable image planes is proposed. For implementing the variable image planes, polymer-dispersed liquid-crystal (PDLC) films and a projector are adopted as a new display system in the integral imaging. Since the transparencies of PDLC films are electrically controllable, we can make each film diffuse the projected light successively with a different depth from the lens array. As a result, the proposed method enables control of the location of image planes electrically and enhances the depth. The principle of the proposed method is described, and experimental results are also presented.